Central Office (CO) telephone systems make up most of the current verbal communications networks of the world. Each CO interconnects thousands of local offices and homes with twoway communications via telephone lines. A CO generally directs a call to a specific telephone number in a home, office, or other facility based on the number dialed by the person or machine that initiates the call. This call-directing function at the CO was in the past performed by a switch board operator who physically plugged in the appropriate wires to the appropriate sockets to make the connection, but it is now generally done by computers. Once that number is reached by the caller, a person at the receiving number answers the telephone, and the caller must verbally ask for the person to whom he wishes to speak. Of course, this person to person request may also be done by a CO operator. In any case, once the receiver gets the call, he or she then must locate the person to whom the caller wishes to speak. Many offices and businesses have PBX type switchboards or other intercom and notification systems for directing calls to specific persons, but most residences do not have such expensive equipment installed.
With the recent dramatic drop in cost of today's home telephones in conjunction with federal law allowing homeowners more unregulated use of telephone lines and extension phones in their homes, many homes now have multiple extension telephones sharing a single line. In a house with, for example, a kitchen telephone and two bedroom telephones, the person answering the telephone usually has to shout to find the proper call receiver. Some houses are equipped with intercom systems to accomplish this function, but most are not. While the house telephone is off the hook and the proper call receiver is being sought, the telephone line is tied up, and no other calls can come in. No low cost method is available today to page for the proper call receiver by using the various existing home telephones as paging devices.